Why PAL and NTSC files play correctly automatically

[Celerorm]

Just wondering, why video files .avi or .mkv play correctly on every computer.

My computer is PAL 50 Hz (25 fps) but it still play content fine of NTSC 60 Hz (23.975 fps).

In VHS era, you have to convert NTSC tapes to PAL somehow before you can watch them, and quality was usually bad.

So why it works directly?

BTW, It seems that all? LCD monitors/televisions has 60 Hz at use, even if my electrial socket gives out 50 Hz.
Why it is so?
But thanks for anwers anyways

[jagabo]

Computers are smart devices and have no problem figuring out how to repeat frames to match the monitor's refresh rate. Old analog equipment wasn't very flexible and had to be designed around specific frame rates to keep costs down.

The biggest issue is that computer (and other modern digital equipment) keeps a digital copy of video frames in memory. Those frames can be output to the monitor as many times as necessary to match the displays frame rate. Analog equipment had no memory -- the analog signal had to be displayed as it was received. There was no way to repeat the last frame or field.